Allow variable jsonpath specifications in JSON_TABLE

Author: Nikita Glukhov

src/backend/parser/gram.y

@@ -845,7 +845,7 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
  */
 %nonassoc	UNBOUNDED		/* ideally should have same precedence as IDENT */
 %nonassoc	ERROR_P EMPTY_P DEFAULT ABSENT /* JSON error/empty behavior */
-%nonassoc	FALSE_P KEEP OMIT PASSING TRUE_P UNKNOWN
+%nonassoc	COLUMNS FALSE_P KEEP OMIT PASSING TRUE_P UNKNOWN
 %nonassoc	IDENT GENERATED NULL_P PARTITION RANGE ROWS PRECEDING FOLLOWING CUBE ROLLUP
 %left		Op OPERATOR		/* multi-character ops and user-defined operators */
 %left		'+' '-'
@@ -14739,7 +14739,7 @@ json_table_error_clause_opt:
 		;
 
 json_table_column_path_specification_clause_opt:
-			PATH json_path_specification			{ $$ = $2; }
+			PATH Sconst								{ $$ = $2; }
 			| /* EMPTY */ %prec json_table_column	{ $$ = NULL; }
 		;
 
@@ -14771,7 +14771,7 @@ json_table_formatted_column_definition:
 		;
 
 json_table_nested_columns:
-			NESTED path_opt json_path_specification
+			NESTED path_opt Sconst
 							json_as_path_name_clause_opt
 							json_table_columns_clause
 				{

src/backend/parser/parse_clause.c

@@ -1059,6 +1059,18 @@ transformRangeTableSample(ParseState *pstate, RangeTableSample *rts)
 	return tablesample;
 }
 
+static Node *
+makeStringConst(char *str, int location)
+{
+	A_Const *n = makeNode(A_Const);
+
+	n->val.type = T_String;
+	n->val.val.str = str;
+	n->location = location;
+
+	return (Node *)n;
+}
+
 /*
  * getRTEForSpecialRelationTypes
  *
@@ -1102,6 +1114,7 @@ transformJsonTableColumn(JsonTableColumn *jtc, Node *contextItemExpr,
 	JsonValueExpr *jvexpr = makeNode(JsonValueExpr);
 	JsonCommon *common = makeNode(JsonCommon);
 	JsonOutput *output = makeNode(JsonOutput);
+	JsonPathSpec pathspec;
 
 	jfexpr->op = jtc->coltype == JTC_REGULAR ? IS_JSON_VALUE : IS_JSON_QUERY;
 	jfexpr->common = common;
@@ -1122,7 +1135,7 @@ transformJsonTableColumn(JsonTableColumn *jtc, Node *contextItemExpr,
 	common->passing = passingArgs;
 
 	if (jtc->pathspec)
-		common->pathspec = jtc->pathspec;
+		pathspec = jtc->pathspec;
 	else
 	{
 		/* Construct default path as '$."column_name"' */
@@ -1133,9 +1146,11 @@ transformJsonTableColumn(JsonTableColumn *jtc, Node *contextItemExpr,
 		appendStringInfoString(&path, "$.");
 		escape_json(&path, jtc->name);
 
-		common->pathspec = path.data;
+		pathspec = path.data;
 	}
 
+	common->pathspec = makeStringConst(pathspec, -1);
+
 	jvexpr->expr = (Expr *) contextItemExpr;
 	jvexpr->format.type = JS_FORMAT_DEFAULT;
 	jvexpr->format.encoding = JS_ENC_DEFAULT;
@@ -1629,6 +1644,7 @@ transformJsonTable(ParseState *pstate, JsonTable *jt)
 	JsonCommon *jscommon;
 	JsonTablePlan *plan = jt->plan;
 	char	   *rootPathName = jt->common->pathname;
+	char	   *rootPath;
 	bool		is_lateral;
 
 	cxt.table = jt;
@@ -1658,7 +1674,7 @@ transformJsonTable(ParseState *pstate, JsonTable *jt)
 	}
 
 	jscommon = copyObject(jt->common);
-	jscommon->pathspec = pstrdup("$");
+	jscommon->pathspec = makeStringConst(pstrdup("$"), -1);
 
 	jfe->op = IS_JSON_TABLE;
 	jfe->common = jscommon;
@@ -1682,10 +1698,19 @@ transformJsonTable(ParseState *pstate, JsonTable *jt)
 
 	cxt.contextItemTypid = exprType(tf->docexpr);
 
+	if (!IsA(jt->common->pathspec, A_Const) ||
+		castNode(A_Const, jt->common->pathspec)->val.type != T_String)
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("only string constants supported in JSON_TABLE path specification"),
+				 parser_errposition(pstate,
+									exprLocation(jt->common->pathspec))));
+
+	rootPath = castNode(A_Const, jt->common->pathspec)->val.val.str;
+
 	tf->plan = (Node *) transformJsonTableColumns(pstate, &cxt, plan,
 												  jt->columns,
-												  jt->common->pathspec,
-												  &rootPathName,
+												  rootPath, &rootPathName,
 												  jt->common->location);
 
 	tf->ordinalitycol = -1;		/* undefine ordinality column number */

src/backend/utils/adt/ruleutils.c

@@ -10124,7 +10124,8 @@ get_json_table_columns(TableFunc *tf, JsonTableParentNode *node,
 								   " FORMAT JSONB" : " FORMAT JSON");
 
 		appendStringInfoString(buf, " PATH ");
-		get_const_expr(colexpr->path_spec, context, -1);
+
+		get_json_path_spec(colexpr->path_spec, context, showimplicit);
 
 		if (colexpr->wrapper == JSW_CONDITIONAL)
 			appendStringInfo(buf, " WITH CONDITIONAL WRAPPER");

src/test/regress/expected/jsonb_sqljson.out

@@ -1832,3 +1832,8 @@ SELECT JSON_QUERY(jsonb '{"a": 123}', '$' || '.' || 'a' WITH WRAPPER);
 SELECT JSON_QUERY(jsonb '{"a": 123}', 'error' || ' ' || 'error');
 ERROR:  bad jsonpath representation
 DETAIL:  syntax error, unexpected IDENT_P at or near " "
+-- Should fail (not supported)
+SELECT * FROM JSON_TABLE(jsonb '{"a": 123}', '$' || '.' || 'a' COLUMNS (foo int));
+ERROR:  only string constants supported in JSON_TABLE path specification
+LINE 1: SELECT * FROM JSON_TABLE(jsonb '{"a": 123}', '$' || '.' || '...
+                                                     ^

src/test/regress/sql/jsonb_sqljson.sql

@@ -835,3 +835,5 @@ SELECT JSON_QUERY(jsonb '{"a": 123}', '$' || '.' || 'a');
 SELECT JSON_QUERY(jsonb '{"a": 123}', '$' || '.' || 'a' WITH WRAPPER);
 -- Should fail (invalid path)
 SELECT JSON_QUERY(jsonb '{"a": 123}', 'error' || ' ' || 'error');
+-- Should fail (not supported)
+SELECT * FROM JSON_TABLE(jsonb '{"a": 123}', '$' || '.' || 'a' COLUMNS (foo int));